1. Field of the Invention
The present invention relates to a compressor, and more particularly to a compressor that is provided with a torque limiter and is suitable for use as a refrigerant compressor in an air-conditioning system mounted on a vehicle.
2. Description of the Related Art
A refrigerant compressor for an air-conditioning system mounted on a vehicle such as an automobile is rotationally driven, while the vehicle is running, by a vehicle-mounted internal combustion engine which is the main power source for driving the vehicle, but if it is required to operate the air-conditioning system when the internal combustion engine has come to a stop by idling-stop control or the like, the compressor is rotationally driven by an electric motor operated by a battery mounted on the vehicle as an auxiliary power source. Such a compressor that is driven selectively by one of plural power sources is called as a composite-drive type compressor or a hybrid drive type compressor.
A compressor is described in Japanese Unexamined Patent Publication (Kokai) No. 11-30182, in which, in order to eliminate the need of rotational power connecting/disconnecting means such as an electromagnetic clutch commonly used as a power transmission mechanism for driving a rotary refrigerant compressor, a one-way clutch is provided between a pulley which receives the rotational power from an internal combustion engine and a rotation shaft of the compressor such that the one-way clutch acts so as to stop the rotation of the pulley when the internal combustion engine has come to a stop and the compressor is to be rotationally driven by an electric motor. This compressor is kept rotating at all times while the internal combustion engine is being driven even if the air-conditioning system needs not be operated. Thus, when the refrigerant needs not be compressed, an electromagnetic valve provided in the passage connecting a discharge chamber to a suction chamber is opened so that the effective displacement volume is reduced substantially to zero.
Generally, there are other cases where a one-way clutch is used in a power transmission mechanism, as described, for example, in Japanese Examined Patent Publication (Kokoku) No. 07-72585, in which a one-way clutch is provided between a pulley (either the crank shaft pulley or the driven side pulley) and a rotation shaft in order to prevent the reduction of service life of a belt due to the minute variation of rotation speed in a reciprocating internal combustion engine, which leads to the reduction of the driving torque so that the crank shaft pulley is driven rotationally in reverse direction by the driven side pulley and excessive tension is produced in the belt on the trailing side, leading to reduction of the service life of the belt. Also, technical means are disclosed in Japanese Unexamined Patent Publication (Kokai) No. 06-129449, where, in a sprag-type one-way clutch which can be used for the above-described purpose and in which power transmission may be hampered by roll-over, the outer ring of the one-way clutch is hardened to prevent occurrence of the deformation of the outer ring.
When a compressor is constructed in this manner, by using a one-way clutch instead of an electromagnetic clutch, such that the rotation shaft of the compressor is always kept rotating while the internal combustion engine is operated, the torque load acting upon the rotation shaft of the compressor may become excessively large in the event of failure or locking of the compressor and, as a result, the belt between a crank shaft pulley of the internal combustion engine and a pulley on the compressor side may be broken, or the internal combustion engine may come to a stop and the vehicle cannot keep running on, or a torque shock may be produced that gives uncomfortable sensation to the passengers in the vehicle.
In order to resolve these problems associated with a compressor having no electromagnetic clutch, it is necessary to provide a member, as described in Japanese Unexamined Patent Publication (Kokai) No. 2001-317456, which breaks when an excess torque load above a predetermined value is applied, somewhere in the power transmission path from the pulley to the rotation shaft of the compressor. However, this may give rise to another problem such as increase of the number of parts, increase of size due to required additional space for providing such a member around the pulley or the like, or complicated shape being required for parts such as pulley. Moreover, in the prior art as described above, the function of a torque limiter is realized by breakage of a member and, as the timing of the occurrence of breakage of the member fluctuates depending upon various factors such as the surface characteristics of the member, metallography of the material, temperature, and age deterioration, there arises another problem that the member may break during normal operation or the member may not break even if the predetermined torque is exceeded.